1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus capable of effectively initializing a laser drive circuit.
2. Discussion of the Related Art
A background electrophotography image forming apparatus such as a printer, a multi-function machine, and so forth generally employs a combination of a laser scanning and a photoconductive drum to initially form an electrostatic latent image. An optical scanning system performing the laser scanning is typically integrated in a housing, and an image forming mechanism is provided with various components arranged around the photoconductive drum. The optical scanning system drives a laser diode (LD) with a modulated signal so that the laser diode emits a modulated laser light beam. The laser beam is deflected by a polygon mirror to scan a photoconductive surface of the photoconductive drum. As a consequence of laser scanning, an electrostatic latent image is formed on the photoconductive drum.
The optical scanning system needs to perform an initial detection on the above-mentioned laser diode so as to maintain an output laser of the laser diode at a constant level. Generally, a photodiode is used for the initial detection of a laser emission amount. For example, Japanese unexamined laid-open patent application publication No. 2004-153118 describes a semiconductor laser drive apparatus which allows a laser diode to light on with a digital data signal from an initialization circuit. For another example, Japanese unexamined laid-open patent application publication NO. 2005-129842 describes a semiconductor laser drive apparatus which can shorten a time period for detecting a differential quantum efficiency in accordance with properties of a laser diode.
The optical scanning system, however, has an inherent drawback. When a laser light beam impinges on a reflection surface of the polygon mirror at an incident angle of approximately 90 degrees, a reflected laser light beam straightly return to the photodiode included in the laser diode. If this happens, the laser diode cannot properly radiate the laser light.